Bleaching.



UNITED STATES PATENT OFFICE.

KARL REINKING AND ERICH DEHN EL, OF LUDWIGSHAFEN-ON-THE-RHINE,

AND HANS LABHARDT, OF MANNHEIM, GERMANY, ASSIGNORS TO" BADISOHE 'ANILIN & SODA FABRIK, OF LUDWIGSHAFEN-ON-THE RHINE, GERMANY, A CORPORATION.

BLEACHING.

i No. 837,730.

Patented nee. 4, 1906.

To all whom it may concern.-

Be it known that we, KARL REINKING, a subject of the Prince Regent of Brunswick, and Enron DEHNEL, a subject of the King of Prussia, German Emperor, residing at Ludwigsh'afen-on-the-Rhine, and HANS LAB- HARDI, a citizen of the Swiss Republic, residing at Mannheim, Germany, doctors of philosophy and chemists, have invented new and useful Improvements in Decolorizing, of which the following is a specification.

It is well known that the alkali salts of formaldehydesulfoxylic acidrongalite C (B. A. S. F.) either alone or in combination with formaldehyde-bisulfite (hydrosulfite NF, orhyraldite A) possess only very slight reducing properties in the cold, whereas when hot they are exceptionally strong reducing a ents. In consequence of this property itias been attempted to make use of them for removing the coloring-matter from dyed rags which are to be used in the manufacture of shoddy. For this purpose, however, the said alkali salts possess certain disadvantages, since their neutral solutions, even when boiling, only exercise a moderate reducing action, and in consequence they have to be used in acid solution. Now the alkali salts of formaldehydesulfoxylic acid are extremely sensitive to acids, and upon warming an acidified solution of such a salt decomposition takes place and sulfur is enerally precipitated and remains in the ber as animpurity, the fiber acquiring a persistent disagreeable odor. Further, in consequence of the said decomposition a great part of the reducing power is lost, it not being used up forthe purpose desired. 'We have dis covered that these disadvantages can be avoided if instead of the alkali salts of formaldehydesulfoxylic acid the diflicultly-soluble basic zinc salt be employed. (See Letters Patent No. 793,610, and application Serial No. 298,861.) This salt on account of its very slight solubility exercises in neutral solution scarcely any reducing action on dyed fiber even at boiling temperature, whereas on the addition of acid an energetic reduction of the coloring-matter takes place without the aforementloned objectionable to be em loyed for the purposes of our invention inc ude acetic acld, especially formic acid. When the aforesaid zincsalt is used in the presence of an acid, only very slight decomposition at the most takes place, so that a glven quantity of difficultly-soluble basic zinc formaldehydesulfoxylate produces a considerably greater effect than the chemically equivalent quantity of the sodium salt. This property of they said basic zinc salt can also be applied in other cases where an acid reduction is desiredfor instance, in removing the natural color from linen, hemp, or jute materials and the like.

The following examples will serve to illustrate how' our mvention can be carried into ractical effect; but our invention is not coned to these examples' The parts are by Weighti Example 1: Pre are a bath containing three (3) arts of" asic zinc formaldehydesulfoxylate and from three (3) to five (5) parts of formic acid for eve one hundred (100) parts of the material to e treated, and then add woolen rags which have previously been treated in the usual manner. Heat the whole slowlyto the boiling-point and continue boiling until a test portion of the liquid does not reduce indigocarmin solution. This generally isthe case after boiling for about ten (10) minutes.

If desired, the acid can be added to the boiling-bath slowly in small portionsat a time, and instead of formic acid another acid for instance, acetic acid or sulfuric acidcan be employed.

Example 2: Stir together five (5) parts of basic zinc formaldehydesulfoxylate and one hundred (100) parts of water and add sulfuric acid to the mixture until the salt is dissolved and the solution has a slight acid reaction. Then introduce into this bath the raw material-for instance, hemp or jute material which has previously been extracted with boiling water and which is still colored with natural coloring-matter-and leave the said material in the bath until the desired effect has been obtained.

decomposition taking place. Acids suitable sulfuric acid, and

The reducing property of the bath does not become entirel exhausted, but the bath can repeatedly be rought up to its original conditlon by the addition of correspondingly smaller quantities of the zinc formaldehydesulfoxylate and acid.

If desired, the bath can be heated even up to the boiling-point during the reaction, pro vided the nature of the material being treat- 10 ed allows this to be done.

Now what we claim is- The rocess for the removal-of coloringmatter om dyed, or naturally-colored, Ina- Witnesses:

ERNEST F. EHRHARDT, J. Auto LLOYD. 

